Method for inspecting the elements of piping systems by electromagnetic waves

ABSTRACT

Electromagnetic waves are driven in the pipe to be inspected in the piping system by a transmitting antenna of a transmitter, to be propagated in the pipe; while a receiving antenna of a receiver is moved outside the pipe along the pipe, to receive leaking electromagnetic waves for inspecting elements of the piping system, and the location concerned of each element of the piping system to be inspected is detected in reference to the location of the receiving antenna where the level of electromagnetic waves received by the receiver becomes a peak. The locations to be inspected are the damaged portions such as holes formed by corrosion, cracks, etc. in the pipes, and the locations of joints, etc. It is also possible to move the transmitting antenna outside along the pipe, while arranging the receiving antenna at proper place in the pipe. Furthermore, it is also possible to move both the transmitting antenna and the receiving antenna in synchronization to effect the above inspection. When either the transmitting antenna or the receiving antenna is moved, the frequency of electromagnetic waves can be a frequency propagated in the pipe or can also be lower than the cut-off frequency. On the other hand, the antenna can be made long and kept in the pipe, to use a frequency lower than the cut-off frequency without moving the antenna.

CROSS REFERENCE TO A RELATED APPLICATIONS

This is a divisional application of co-pending application Ser. No.08/687,450 filed Aug. 15, 1996.

TECHNICAL FIELD

The present invention relates to a method for inspecting the pipingsystems used to supply city gas, etc. mainly buried under roads, etc. orinstalled in the walls, floors, etc. of buildings, hence not exposedoutside, by use of electromagnetic waves, to detect, for example,damaged portions such as holes formed by corrosion in the pipes as oneof an element of piping system, and the locations of joints as anotherelements of piping system, etc.

BACKGROUND OF THE INVENTION

The gas leak from a hole formed by corrosion, etc. in a gas pipe notexposed outside like a buried pipe in the piping system of a city gassupply network is conventionally inspected by using various methods suchas the sense of smell or a gas detector, or boring work in combinationwith the foregoing means, etc. If gas leak is detected in reference tothe smell or in periodical inspection, the ground is dug or the wall isremoved, to exchange or repair the gas pipe.

However, in the conventional methods, since any component of the gasitself or an odorous component added beforehand to the gas which leaksand diffuses from a damaged portion of the gas pipe is detected by usinga gas detector or the human sense of smell, to identify the fact of leakand the location of leak, the occurrence of gas leak and its locationcannot always accurately detected.

For example, if a cavity is formed in parallel to a gas pipe installedunderground or inside a wall, etc., it can happen that the gas leakingfrom a damaged portion of the gas pipe migrates through the cavity anddiffuses into air or indoor, etc. at a position apart from the damagedportion, and in this configuration, it can happen that the positionapart from the actually damaged portion is detected as the damagedportion by error. If excavation or wall removal, etc. is effected asmentioned above based on the wrong information, the work is wasteful,and second and even third work may be required disadvantageously.Furthermore, if the gas leaking from a damaged portion of a gas pipe isretained near the damaged portion without diffusing in air or indoor,etc., the leak itself may not be able to detected.

As described above, the method of inspecting the occurrence of leak andthe damaged portion by detecting any component of the gas itself or theodorous component added beforehand to the gas leaking and diffusing fromthe damaged portion cannot always accurately detect the occurrence ofleak and its location.

On the other hand, one of conventional general inspection methods fordetecting the damage of metallic structures is ultrasonic flawdetection, but it is difficult to apply this method for inspection ofpiping systems not exposed, for such reasons that the probe must be keptin tough with the object to be inspected, and that flaw detection for along distance cannot be made.

An object of the present invention is to overcome the above mentioneddisadvantages of the conventional inspection methods, and to provide aninspection method which can relatively accurately detect damagedportions of pipes such as holes formed by corrosion, when applied to theinspection of elements of piping systems, particularly metallic pipingsystems not exposed.

Another object of the present invention is to provide an inspectionwhich can measure the distances of piping systems to damaged portionsand can detect the locations and states of some joints as other elementsof piping systems, in addition to the detection of damaged portions ofpipes.

DISCLOSURE OF THE INVENTION

The inspection method of the present invention comprises the steps ofdriving electromagnetic waves at a proper place of the pipe to beinspected of a piping system, by a transmitting antenna of atransmitter, for propagating the electromagnetic waves in the pipe;moving a receiving antenna of a receiver along the pipe outside, toreceive leaking electromagnetic waves for inspecting the elements of thepiping system; and detecting an intended location of an element of thepiping system inspected, in reference to the location of the receivingantenna at which the level of received electromagnetic waves becomes apeak.

In this configuration, the electromagnetic waves propagated in a pipe donot usually leak outside, but if there is any damaged portion such as ahole formed by corrosion or crack, etc. in the pipe, the electromagneticwaves leak from the portion, and are detected by the receiving antenna,to allow the damaged portion to be identified. The leak ofelectromagnetic waves may occur not only such damaged portions but alsoat joints, and in this configuration, joints can also be detected. Thelevel of received leaking electromagnetic waves in the receiver becomeshighest when the receiving antenna is at a location nearest to anyobject to be detected such as a damaged portion or joint if thereceiving antenna is non-directional or moves in parallel in itsdirection. So, at the location of the receiving antenna at which thelevel of the received waves becomes a peak, the damaged portion or jointlocation of the piping system buried under a road, etc. or installed inthe wall or under the floor, etc. of a building, hence not exposedoutside can be accurately detected.

In the present invention configured as above, the transmitting antennais provided as a coaxially formed antenna with a probe protruded at thecenter and external threads formed around its outside member isinstalled in the antenna installation hole which is a hole drilled withinternal threads formed in the wall of the pipe to be inspected of apiping system. In another version, an end of the pipe to be inspected ofa piping system is cut off, and a coaxially formed antenna with a probeprotruded coaxially is mounted on the cover to close the end, said coverbeing installed at the end. In a further other version, a probe isprotruded inside the cover to close the central branch opening of a Teeinstalled on the extension of the pipe to be inspected of a pipingsystem, and the probe and an electromagnetic wave generator areconnected by a coaxial cable, with the probe located in the Tee when thecover is installed. In a still further other version, a loop isprotruded inside the cover to close the central branch opening of a Teeinstalled on the extension of the pipe to be inspected of a pipingsystem, and the loop and an electromagnetic wave generator are connectedby a coaxial cable, with the loop located in the Tee when the cover isinstalled.

By any of the above means, the transmitting antenna can be easilyinstalled in the pipe to be inspected of a piping system, and especiallywhen a Tee is installed on the extension of a pipe of the piping system,pipe drilling work and cutting work are not required. Therefore, whenthe piping system to be inspected is, for example, a city gas supplysystem, the installation of the transmitting antenna and subsequentinspection as described above can be effected without stopping thesupply of gas. Also when the transmitting antenna is installed in a holedrilled in the wall of a pipe, the antenna can be installed withoutstopping the supply of gas. These means for installing the transmittingantenna can also be applied to the methods described later forinstalling the receiving antenna at a proper place of a pipe of a pipingsystem.

In the present invention, the receiving antenna is moved outside thepiping system as described before, and for inspection, the transmittingantenna is moved inside the pipe of the piping system in connection withthe movement of the receiving antenna, for generating electromagneticwaves.

In this configuration, the level of the electromagnetic waves receivedby the receiver near the location to be detected changes greatly to makethe peak more outstanding, for enhancing the detection accuracy of thelocation to be detected in reference to the peak.

In the above method of the present invention, the frequency ofelectromagnetic waves is continuously or stepwise changed over time.

Since this does not allow any fixed electromagnetic field distributionto be formed in the pipe, the leak of electromagnetic waves from thelocation to be detected can be reliably identified, to allow reliabledetection of the location to be detected.

In the present invention, the reception of leaking electromagnetic wavesby the receiver is effected when the transmission of electromagneticwaves by the transmitter is in ON state and also when the transmissionof electromagnetic waves by the transmitter is temporarily in OFF state,to identify the leaking electromagnetic waves by comparing the signalsreceived in OFF state with the signals received in ON state. The ON-OFFcontrol means can be provided in the transmitter, and a remote controlswitch for the ON-OFF control means can be provided in the receiver, toallow the ON-OFF control means to be operated from the receiver.Otherwise, the ON-OFF control means can be provided in the transmitterfor ON-OFF control from the transmitter, and the signals synchronouswith the ON-OFF actions can be transmitted to the receiver, to allow theON and OFF states to be detected by the receiver.

In this configuration, the receiving antenna outside the piping systemcan reliably identify whether any electromagnetic waves received areleaking from said location concerned or external noise only.

In the present invention configured as above, the electromagnetic wavespropagated by the transmitter in the piping system to be inspected aremodulated. The modulation of electromagnetic waves can be used as amethod for changing the frequency of electromagnetic waves over timedescribed before and also as a method for turning on and off thetransmission of electromagnetic waves by the transmitter.

In this configuration, if the electromagnetic waves as carrier waves aremodulated by human recognizable information signals such as audiosignals or visual signals, whether the electromagnetic waves received bythe receiver are the electromagnetic waves transmitted by thetransmitter or noise can be easily discriminated.

In another version of the present invention, the transmitting antenna ofthe transmitter can be moved along a pipe outside the piping system tobe inspected, to transmit electromagnetic waves from the outside of thepiping system. In this case, the receiving antenna of the receiver isfixed at a proper place of the pipe, or is moved in relation with themovement of the transmitting antenna, to receive the electromagneticwaves introduced into the piping system from outside, for inspecting theelements of the piping system. This method can be used as a method forchanging the frequency of electromagnetic waves over time, as a methodfor turning on and off the transmission of electromagnetic waves by thetransmitter and also as a method for modulating the electromagneticwaves respectively described before.

In this configuration, the electromagnetic waves transmitted fromoutside are introduced into the piping system from the location to bedetected, propagated in the pipe and received by the receiver throughthe receiving antenna, to allow the location concerned to be identified.Since the level of the electromagnetic waves introduced from thelocation to be detected and received by the receiver becomes highestwhen the transmitting antenna is at a location nearest to the locationto be detected, the location to be detected of the piping system can beaccurately detected in reference to the location of the transmittingantenna at which the level of received electromagnetic waves becomes apeak.

In the present invention, the electromagnetic waves transmitted into apipe by the transmitter are modulated, and the electromagnetic wavesreceived by the receiver and the electromagnetic waves transmitted bythe transmitter are compared in terms of modulated signals, to obtainthe time difference. From the time difference, the propagation timecorresponding to the distance remaining after subtracting thepropagation distance from the transmission point to the leak point issubtracted, to measure the propagation time of electromagnetic wavesfrom the transmission point to the leak point, for obtaining thedistance of the piping system from the transmission point to the leakpoint. In this case, the time difference can be measured in reference tothe phase difference between the electromagnetic waves detected by thetransmitter and those transmitted by the transmitter in terms ofmodulated signals, and pulse compression can be applied to theelectromagnetic waves when they are transmitted to the transmitter andto the electromagnetic waves when they are received by the receiver.

As described above, the location to be detected such as a damagedportion or a joint of a pipe in a piping system can be detected, and inaddition, the distance from a reference location properly set in thepiping system to a leak point can be measured.

In the methods described above, the electromagnetic waves transmitted bythe transmitter are propagated through a pipe of the piping systemconcerned at a frequency higher than the cut-off frequency for the pipeused as a wave-guiding channel of electromagnetic waves, but in thefollowing two versions of the present invention, the frequency is keptlower than the cut-off frequency.

In one of the versions of the present invention, while the transmittingantenna of the transmitter is moved in the pipe to be inspected of apiping system, electromagnetic waves are transmitted at a frequencylower than the cut-off frequency for the pipe used as a wave-guidingchannel of the electromagnetic waves, and the receiving antenna of thereceiver is moved in relation with the movement of the transmittingantenna, to receive leaking electromagnetic waves for inspection ofelements of the piping system. In this case, the location to be detectedof an element of the piping system to be inspected is detected inreference to the location of the transmitting antenna at which the levelof the electromagnetic waves received by the receiver becomes a peak.

In this configuration, since the electromagnetic waves from thetransmitting antenna are attenuated greatly without being propagated inthe pipe, the quantity of the electromagnetic waves leaking from thelocation to be detected such as a damaged portion or joint of the pipebecomes largest when the transmitting antenna is nearest to the locationto be detected. Therefore, the level of electromagnetic waves receivedby the receiver is very large when the transmitting antenna is near thelocation to be detected, to make the peak more outstanding, therebyenhancing the detection accuracy of the location concerned by the peak.

In the other version of the present invention, while the transmittingantenna of the transmitter is moved along a pipe outside the pipingsystem to be inspected, electromagnetic waves are transmitted fromoutside the piping system at a frequency lower than the cut-offfrequency for the pipe used as a waveguiding channel of theelectromagnetic waves, and the receiving antenna of the receiver ismoved in the pipe in relation with the movement of the transmittingantenna, to receive the electromagnetic waves introduced into the pipefrom outside, for inspection of elements of the piping system. In thiscase, the location to be detected of an element of the piping system tobe inspected is detected in reference to the location of the receivingantenna at which the level of electromagnetic waves received by thereceiver becomes a peak.

In this configuration, since the electromagnetic waves introduced fromthe transmitting antenna through the location to be detected are notpropagated in the pipe, the quantity of leak is largest when thereceiving antenna is nearest to the location to be detected. Therefore,also in this case, the level of electromagnetic waves received by thereceiving antenna becomes very large when the receiving antenna is nearthe location to be detected, to make the peak more outstanding, forenhancing the detection accuracy of the location to be detected by thepeak.

Also in these two versions of the present invention as in the previousversions of the present invention, if the electromagnetic waves ascarrier waves are modulated by proper information signals, whether theelectromagnetic waves received are the electromagnetic waves transmittedby the transmitter or noise can be easily discriminated.

In a still further other version of the present invention, a longtransmitting antenna composed of many directional radiating partsarranged in the directions perpendicular to the axis and ranged in theaxial direction is inserted in an inspection range of the pipe to beinspected of a piping system, to radiate electromagnetic waves in thepipe by the transmitter, and a receiving antenna of a receiver is movedalong the pipe in the inspection range outside the piping system, toreceive leaking electromagnetic waves, for inspection of elements of thepiping system. In this case, the location to be detected of an elementof the inspection system to be inspected is detected in reference to thelocation of the receiving antenna at which the level of electromagneticwaves received by the receiver becomes a peak.

In a still further other version of the present invention, contrary tothe above version, a long receiving antenna composed of many directionalradiating parts arranged in the directions perpendicular to the axis andranged in the axial direction is inserted in an inspection range of thepipe to be inspected of a piping system, and is connected with areceiver, and a transmitting antenna of a transmitter is moved in theinspection range outside the piping system to be inspected, to transmitelectromagnetic waves from outside the piping system, so that thereceiver may receive the electromagnetic waves introduced from outsideinto the pipe. In this case, the location to be detected of an elementof the piping system to be inspected is detected in reference to thelocation of the transmitting antenna at which the level ofelectromagnetic waves received by the receiver becomes a peak.

By any of the above means, as in these two inventions described before,the frequency of the electromagnetic waves transmitted by thetransmitting antenna can be lower than the cut-off frequency determinedby the diameter of the pipe of the piping system, to allow to decresethe influence of the attenuation of the electromagnetic waves by thesoil or concrete, etc. for inspecting the buried piping system.Moreover, the necessity of the synchronous movements of the transmittingantenna and the receiving antenna is eliminated in comparison with theseaforesaid two inventions.

In the above two versions of the present invention, the long antenna canbe a long helical antenna, leakage coaxial cable or twisted pair leakagecable with its directions kept perpendicular to the axis.

In the present invention described above, an element to be inspected ofa piping system is, first of all, a pipe, and in this case, the locationto be detected is a damaged portion such as a hole formed by corrosionin the pipe. Another element to be inspected is a joint not exposed, andin this case the location to be inspected is the location of the jointitself.

Furthermore, in the present invention, when a joint is the element to beinspected, not only its location but also the condition of the joint canbe estimated in reference to the level of electromagnetic waves receivedby the receiver.

In the present invention as described above, the transmitter can beprovided with a device for adjusting the intensity of theelectromagnetic waves transmitted, and if the adjusting device is usedto adjust in response to the level of electromagnetic waves received bythe receiver for example, the peak can be easily detected at a properlevel of electromagnetic waves received.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration conceptually showing an embodiment of thepresent invention.

FIG. 2 is an illustration conceptually showing another embodiment of thepresent invention.

FIGS. 3 and 4 are graphs showing the results of tests to detect adrilled hole of a test pipe by applying the present invention.

FIG. 5 is a sectional view showing an antenna attached to a pipe.

FIG. 6 shows an essential portion of FIG. 5.

FIG. 7 is an illustration conceptually showing a method for installingan antenna in a piping system.

FIG. 8 is a sectional view showing a configuration of an antenna inwhich the installation method of FIG. 7 is applied.

FIGS. 9 through 12 are sectional views showing other configurations ofan antenna in which the installation method of FIG. 7 is applied.

FIG. 13 is an illustration conceptually showing a tester for inspectingthe leak of electromagnetic waves through a joint.

FIG. 14 is a graph showing the results of a test in FIG. 13.

FIG. 15 is an illustration conceptually showing the action of distancemeasurement in a piping system.

FIGS. 16 through 18 show waveforms of electromagnetic waves transmittedfrom a transmitting antenna.

FIG. 19 is an illustration conceptually showing a pipe inspection actionwith the transmission of electromagnetic waves turned on and off.

FIG. 20 is an illustration conceptually showing another pipe inspectionaction with the transmission of electromagnetic waves turned on and off.

FIG. 21 is an illustration conceptually showing the results ofinspection actions of FIGS. 19 and 20.

FIG. 22 is an illustration conceptually showing an inspection actionwith an antenna moved.

FIG. 23 is a perspective view showing some components.

FIG. 24 is an illustration conceptually showing an inspection action bya long antenna.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

The present invention is described below in more detail in reference tothe attached drawings.

FIG. 1 conceptually shows an embodiment of the present invention. Symbol1 denotes a pipe as an element to be inspected of a piping system, andthe pipe 1 in this drawing is buried underground 2. FIG. 2 conceptuallyshows another embodiment, and the pipe 1 in this drawing is installedinside a wall 3 of a building.

The piping systems which can be inspected by applying the presentinvention include city gas supply systems of chemical plants,also pipingsystems of chemical plants, piping systems for heat exchanges ofelectric power plants, water supply pipes, etc., and the presentinvention can be effectively applied to piping systems buriedunderground such as under roads or installed in the walls or under thefloors of buildings, hence not exposed outside.

Symbol 4 generally denotes an inspection apparatus to which the presentinvention is applied. The inspection apparatus 4 is generally composedof a transmitter 5 and a receiver 6, and the transmitter 5 is composedof a transmitter proper 7 and a transmitting antenna 8 to be installedat an end of the pipe 1, i.e., a means for driving electromagnetic wavesinto the pipe 1. The receiver 6 is composed of a receiver proper 9 and areceiving antenna 10, and the receiving antenna 10 can move.

To describe the configuration of the illustrated transmitting antenna 8,the transmitting antenna 8 has an antenna proper 13 protruded at thecenter inside a metallic cover 11 to close the end of the pipe 1 andconnected with the transmitter proper 7 through a coaxial cable 12, andwhen the transmitting antenna 8 is fixed at the end of the pipe 1 by ascrew 14 provided at a proper place of the cylindrical portion of thecover 11, the antenna proper 13 is arranged almost at the center of thepipe 1. The antenna proper 13 is a probe or loop, etc. which exciteselectromagnetic waves, to propagate them in a predetermined mode. Theother most preferred embodiments of the transmitting antenna 8 (orreceiving antenna) will be described later in detail.

The receiving antenna 10 can be moved manually or on a carriage, etc.Furthermore, the receiving antenna 10 can be moved separately from thereceiver proper 9 or can be mounted integrally with the receiver proper9, to be moved with the receiver proper 9.

In the above configuration, when the pipe 1 buried underground as shownin FIG. 1 or the pipe 1 installed in the wall 3 as shown in FIG. 2 isinspected, the pipe 1 is cut off at a portion exposed in space, etc. onan extension (or a branch) of the pipe 1, and the transmitting antenna 8is installed at the end. Then, electromagnetic waves are supplied fromthe generation means of the transmitter proper 7 through the coaxialcable 12 to the transmitting antenna 8, and are driven in the pipe 1 ina mode corresponding to the arrangement of the transmitting antennaproper 13, etc., to be propagated in the pipe 1. That is, ifelectromagnetic waves of a predetermined frequency are supplied from thetransmitter proper 7 to the transmitting antenna 8, the pipe 1 acts as awave guiding channel similar to a circular waveguide for theelectromagnetic waves, and the electromagnetic waves can be propagatedin a predetermined mode at a frequency higher than the cut-offfrequency.

For example, when the electromagnetic waves are driven in TE₁₁ modewhich is the propagation mode of the lowest order by the transmittingantenna proper 13, the frequency of the electromagnetic waves suppliedto the transmitting antenna proper 13 is made higher than the cut-offfrequency represented by the following formula:

    Cut-off frequency=Light velocity/Cut-off wavelength≈Light velocity/{1.706×Inner diameter of pipe 1}

For example, the cut-off frequency of a pipe of 100 mm in inner diameteris about 1.8 GHz, the cut-off frequency of a pipe of 80 mm in innerdiameter, about 2.2 GHz, and the cut-off frequency of a pipe of 50 mm ininner diameter, about 3.5 GHz. The cut-off frequencies are peculiar toTE₁₁ mode, and in other propagation modes such as TE₀₁, TM₀₁, . . .modes, respectively different peculiar cut-off frequencies exist.

While electromagnetic waves are propagated in the pipe 1 by thetransmitter 5, the receiving antenna 10 of the receiver 6 is moved alongthe pipe 1 outside, for receiving the electromagnetic waves. To move thereceiving antenna 10 along the pipe 1 buried underground 2 or installedin the wall 3, etc., hence not exposed, a piping diagram or designdrawing, or a pipe locator, etc. can be used.

The electromagnetic waves propagated in the pipe 1 as described above donot leak outside in the normal portions of the pipe 1, but if there isany damaged portion 15 such as a hole formed by corrosion or a crack,etc., they leak from the portion to outside.

Therefore, the damaged portion 15 can be detected by receiving theleaking electromagnetic waves by the receiver 6 through the receivingantenna 10. The level of the electromagnetic waves received by thereceiver 6 is highest when the receiving antenna 10 is nearest to thedamaged portion 15 if the receiving antenna 10 is non-directional or ifthe receiving antenna 10 is sharply directional and moved in parallelwith its direction turned toward the pipe 1. Therefore, the location ofthe receiving antenna 10 at which the level of electromagnetic wavesreceived by the receiver 4 becomes a peak can be detected as thelocation of the damaged portion 15. That is, when the pipe 1 is buried,the location below the receiving antenna 10 at which the level ofelectromagnetic waves received becomes a peak can be identified as thelocation of the damaged portion 15, and also when the pipe 1 isinstalled in the wall 3, etc., the location can be identified similarly.

A test pipe of 100 mm in inner diameter with a 30 mm dia. hole drilledas an artificial defect on the top side was buried under a 10 cm thickconcrete layer (with reinforcing bars at the bottom), 10 cm thickcrushed stone layer and 10 cm thick soil layer in this order from theground surface, and from the pipe end, electromagnetic waves of 2 GHz infrequency and 25 dbm were driven and propagated, while the receivingantenna was moved on the ground surface in the axial direction of thepipe and in the direction perpendicular to the axis, to receive theelectromagnetic waves leaking from the hole of the pipe. The levelsmeasured are shown in FIGS. 3 and 4. FIG. 3 shows a case of moving theantenna in the axial direction of the pipe, and FIG. 4, a case of movingthe antenna in the direction perpendicular to the axis. In both thecases, the distance 0 on the abscissa indicates that the receivingantenna arrived at the location right above the hole.

From the results, it can be seen that since the level of electromagneticwaves received becomes highest, i.e., a peak when the receiving antennais nearest to the hole, the location of the hole can be detected inresponse to the peak.

The level of electromagnetic waves received can be confirmed inreference to the reading on a level meter or the volume or frequency canbe changed in response to the level of electromagnetic waves received,to allow confirmation in reference to sound.

Furthermore, if the electromagnetic waves driven and propagated in thepipe are modulated by human recognizable information signals such asaudio signals or visual signals by the transmitter proper 7, to containthe information signals, and demodulated by the receiver proper 9 foroutput, then the output allows easy confirmation that the receivedelectromagnetic waves are predetermined electromagnetic wavesdistinguished from noise. This can be achieved by letting thetransmitter proper 7 have such components as a modulator and amplifier,and the receiver proper 9 have such components as a detector,demodulator, amplifier, monitor, speaker, etc. These are not illustratedin the drawings.

On the other hand, in the above inspection action, it is preferable thatthe electromagnetic waves leaking from the damaged portion 15 of thepipe 1 by the receiver 6 always at a proper receiving level not affectedby the environment where the pipe 1 is installed. If the pipe 1 isburied underground, it may be buried at a different depth or indifferent soil, and if the pipe 1 is installed in the wall, it may bedifferently apart from the receiving antenna while the material existingbetween them may be different. Therefore, if electromagnetic waves aretransmitted always at the same level and received at the samesensitivity, the level of electromagnetic waves received cannot bealways appropriate.

So, the transmitter 5 is provided with a device (not illustrated) foradjusting the intensity of the electromagnetic waves to be transmittedfrom it. The adjusting device allows level adjustment to ensure reliableinspection without making the level transmitted too high to suit thecapacity of the receiver or without affecting the surrounding as noise.In this configuration, in the beginning of inspection, theelectromagnetic waves transmitted from the transmitter 5 are set at ahigh level, and the receiving sensitivity of the receiver 6 is also setat a high level. If the electromagnetic waves are always received inthis state, the level transmitted is lowered, or the receivingsensitivity is lowered to conduct the inspection as described above.

As a result of the inspection, if the electromagnetic waves are receivedin a wide moving range of the receiving antenna 8, not allowing the peakof the level of electromagnetic waves received to be identified, thelevel transmitted is gradually lowered, to narrow the receiving range ofthe electromagnetic waves, for detection of a peak. In this way, theleak portion of electromagnetic waves, i.e., the location of the damagedportion 15 can be accurately detected. The adjustment of the leveltransmitted can also be effected in response to the level ofelectromagnetic waves received, by connecting the transmitter 5 and thereceiver 6 by any wireless or wired communication means.

As described above, the frequency of the electromagnetic waves suppliedto the transmitting antenna 8 are only required to be properly higherthan the cut-off frequency corresponding to the propagation mode, butsince a higher frequency is attenuated more in soil generally, thefrequency is preferably set at a level as low as possible in thisregard. Therefore, when the element to be inspected of a piping systemis a buried pipe, the frequency of the electromagnetic waves driven andpropagated in the pipe is preferably closer to said cut-off frequency.However, since there may be a pipe smaller in inner diameter than theother pipes of the piping system, the frequency of electromagnetic wavesis preferably properly higher than the cut-off frequency to allowpropagation also in the pipe.

Other embodiments of the transmitting antenna for driving andpropagating electromagnetic waves to the pipe 1 to be inspection aredescribed below.

In the transmitting antenna shown in FIGS. 5 and 6, a hole is drilled inthe wall of the pipe 1 to be inspected of a piping system, and internalthreads are formed in the hole, for use as an antenna installation hole16. A coaxially formed antenna 20 with a probe 17 protruded at thecenter and external threads 19 formed around an outside member 18 isfitted in the antenna installation hole 16 by keeping the external andinternal threads engaged with each other, to locate the probe 17 in thepipe 1. At the rear of the outside member 18, a coaxial connector 21 isprovided.

In this configuration, since the pipe 1 is not required to be cut offunlike the case shown in FIG. 1, the transmitting antenna can beinstalled easily. Furthermore, if the pipe 1 is a city gas supply pipe,the transmitting antenna can be installed without stopping gas supply.

FIGS. 7 through 12 show other embodiments of the transmitting antennadifferent from the above.

FIG. 7 typically shows the entire configuration where the transmittingantenna is applied to the detection of a leak point in a gas pipe.

Symbol 22 denotes a Tee pre-installed around the pipe 1, and the centralbranch opening 23 the Tee 22 is closed by a threaded cover 24. In thisembodiment, the cover 24 is used to form a transmitting antenna sectionas an driving means.

FIGS. 8 through 12 concretely show embodiments of the transmittingantenna section.

In FIG. 8, symbol 25 denotes a support, and 26 denotes a lock nut. Theyare engaged with each other by threads 27. The threads 27a of the locknut 26 are inserted inside from an installation hole 28 formed at thecenter of the cover 24 and engaged, by tightening, with the threads 27bof the support 25 arranged inside, so that the installation hole 28 ofthe cover 24 may be arrested by the collar 28 of the lock nut 26 and thesupport 25. Prior to the threaded engagement, the lock nut 26 has thetip a coaxial cable 12 inserted, to have a central lead 29 protruded,and the braid of a shielded wire 30 is spread along a clamp 31. When thethreaded engagement is achieved, a washer 32 and a gasket 33 are put on,and said tightening bring the spread shielded wire 30 into pressurecontact with the inner wall of the support 25 to achieve installation.On the other hand, the central lead 29 has a linearly formed probe 17bonded at its tip, and the probe 17 is supported at the center of thesupport 25 by an insulator 34. In this configuration, the threads 35a ofthe cover 24 are engaged with the threads 35 of the central branchopening 23 of the Tee 22 by tightening, to close the opening 23. Thisaction keeps the probe 17 in the Tee 22.

In this case, if a shielding material 37 like an O ring made of aconductive rubber or soft metal, etc. is put between the end of theopening 23 and the inside of the cover 24, when the cover 24 istightened by engagement between the threads 35a and 35b, the shieldingmaterial 37 is kept in pressure contact with the end of the opening 23and the inside of the cover 24, to form a shielding portion againstelectromagnetic waves. So, the leak of electromagnetic waves from thedriving portion can be perfectly prevented. Another shielding portioncan be formed by installing a shielding material at the engaging portionbetween the threads 35a and 35b. For example, after the threads 35b ofthe central branch opening 23 of the Tee 22 have had filaments made of asoft metal wound around them, or have been coated with a conductivecompound, the threads 35a can be engaged with the threads 35b, to keepthe deformed filaments or conductive compound in the clearance betweenthe threads 35a and 35b, to form a shielding portion.

In this configuration, if electromagnetic waves are supplied from thetransmitter proper 7 by the coaxial cable 12 to the transmitting antenna13, the electromagnetic waves in the mode corresponding to the electricfield by the probe 17 are driven in the Tee 22 and propagated from theTee 22 to the pipe 1. Thus, the pipe 1 can propagate the electromagneticwaves in a mode similar to a circular waveguide. In the case of FIG. 8,an electromagnetic field of TM₀₁ mode is formed for propagation. If adamaged portion 15 such as a through hole exists in the pipe 1, theelectromagnetic waves propagated in the pipe 1 leak outside from thedamaged portion 15, and the leaking electromagnetic waves are receivedthrough the receiving antenna by the receiver proper 9, to detect thedamaged portion 15.

FIG. 9 shows a modified example of FIG. 8. In this configuration, theprobe 17 is differently formed from that of FIG. 8. The probe 17 of FIG.9 is not simply linearly formed unlike that of FIG. 8, but is formedlike T with its tips turned in the axial direction of the Tee 22. Sincethe other parts are identical with those of FIG. 8, they are given thesame symbols for avoiding double explanation.

FIG. 10 shows a configuration with a loop 36 protruded inside the cover24, instead of the probe of FIG. 8. The loop 36 is formed by connectinga conductor between the tip of the central lead 29 and the tip of thesupport 25. Since the other parts are identical with those of FIG. 8,they are given the same symbols for avoiding double explanation. In thisembodiment, the loop 36 has its axial direction kept in the tangentialdirection of the inside circle of the Tee 22, and in this configuration,an electromagnetic field of TM₁₀ mode is formed for propagation in thepipe 1 as in FIG. 8.

FIG. 11 is a modification example of FIG. 10. This configuration isdifferent from that of FIG. 10 only in the direction of the axis of theloop 36. So as in the above cases, the other parts are given the samesymbols for avoiding double explanation. In this embodiment, the loop 36has its axial direction kept in the axial direction of the Tee 22, andin this configuration, an electromagnetic field of TE₀₁ mode is formedin the pipe 1 for propagation.

FIG. 12 is a modification example of FIG. 8. In this configuration,unlike the above configurations, the cover 24 is threadedly engaged withthe inside of the opening 23. Symbol 38 is a support corresponding tothe support 25 of FIG. 1, and the support 38 has threads 39a formedaround it which are engaged with the threads 39b formed inside thecentral branch opening of the Tee 22. The support 38 also has a collar40 at one end. The other parts are the same as in FIG. 8 and are giventhe same symbols to avoid double explanation.

The mechanism for supporting the coaxial cable 12 by the cover 24, thestructure of the probe 17 and the loop 36 at the tip of the coaxialcable 12, the mechanism for supporting the probe and the loop 36, etc.can be those as adopted in the conventional coaxial waveguidetransducers, etc.

In the above embodiments of the transmitting antenna 13, sinceelectromagnetic waves are driven from the Tee 22 installed on theextension of the pipe 1 into the pipe 1, it is not necessary to cut offat one end of the pipe for excitation, and therefore it is not necessaryto stop gas supply if any of the above embodiments is applied to thepiping system for a city gas supply network. Furthermore, the leak ofelectromagnetic waves from the Tee 22 as an driving section can bereliably prevented.

In the inspection method described above, electromagnetic waves aredriven from the transmitting antenna 13 of the transmitter 5 into thepipe 1 for propagation, and the electromagnetic waves leaking from thedamaged portion 15 are received by the receiver 6 through the receivingantenna moved along the pipe 1 outside the pipe 10. Contrary to thismethod, it is also possible to move the transmitting antenna 13 of thetransmitter along the pipe 1 outside the piping system to be inspected,while transmitting electromagnetic waves toward the pipe 1 from outsidethe piping system, for receiving them by the receiving antenna 10 of thetransmitter 6 installed at a proper place of the pipe 1, even thoughthis method is not illustrated in the drawings.

According to this method, the electromagnetic waves transmitted fromoutside enter the piping system through the damaged portion 15, and arepropagated in the pipe 1, to be received by the receiver through thereceiving antenna, to allow the existence of the damaged portion to bedetected. Since the level of the electromagnetic waves entering from thedamaged portion and received by the receiver is highest at a locationwhere the transmitting antenna is nearest to the damaged portion, thelocation of the damaged portion in the piping system can be accuratelydetected as the location of the antenna at which the level ofelectromagnetic waves received becomes a peak.

In this method, the transmitter and the receiver can be composed in anyway as described before, and the receiving antenna can be selected fromthose examples of the transmitting antenna described above.

In the above method, the receiving antenna can be moved in relation withthe movement of the transmitting antenna, without being fixed in thepipe, to receive the electromagnetic waves entering the piping systemfrom outside, for inspection of elements of the piping system. In thiscase, in addition to the location of the transmitting antenna at whichthe level of electromagnetic waves received becomes a peak, the locationof the receiving antenna can also be taken into account for accuratelydetecting the damaged portion 15.

In the above description, the portions where electromagnetic waves leak,i.e., the portions examined for identification of location are damagedportions 15 such as holes formed by corrosion and cracks in the pipe.However, joints of a piping system can also be detected.

FIG. 13 shows a system for measuring the leak of electromagnetic wavesfrom a joint 41 in a piping system with joints. Symbol 42 is a networkanalyzer which drives electromagnetic waves on the transmission side andmeasures the level of electromagnetic waves received with the receivingantenna 10 on the receiving side located near the joint 41. A pipingsystem has pipe line sections of 40 mm in minimum diameter, and in thesesections, and the cut-off frequency of electromagnetic waves in thesesections is about 4.3 GHz.

FIG. 14 shows the results of measurement. It can be seen that at higherthan about 4.3 GHz close to the above cut-off frequency, electromagneticwaves leak from a joint.

If the above inspection method is applied to a piping system withjoints, electromagnetic waves leak through a rubber ring or gasket whenthe joint is a mechanical joint, or through a gasket if a flange joint,or through a non-conductive member such as a shielding material if ascrew joint.

In this case, since electromagnetic waves are propagated for arelatively long distance in a pipe to leak slightly at every joint, theexcitation of electromagnetic waves at one place allows the detection ofcontinual plural joints, and in reference to each peak in the level ofelectromagnetic waves received by the receiver, the location of thejoint can be detected. In this case, if the receiving antenna is sharplydirectional, it can be moved along the pipe 1 (the route in which thepipe 1 is estimated to be buried in reference to any informationmaterial such as drawing), while the direction is properly changed todetect a peak, the location of the joint can be accurately detected inreference to the direction of the receiving antenna corresponding to thepeak, and the influence of external noise can be minimized. However, ifthe receiving antenna used is non-directional or weakly directional, itcan be moved along the pipe, and the location at which the level ofelectromagnetic waves received becomes a peak can be detected as thelocation right above the joint.

On the other hand, since the quantity of leaking electromagnetic wavesincreases if the joint is loosely tightened, the looseness of a jointcan also be detected in reference to the level of electromagnetic wavesreceived. At a particular joint, if the receiving conditions such as thedistance from the receiving antenna, direction, etc. are the same, thelevel of electromagnetic waves leaking from the joint and receiveddepends on the looseness. So, if the level measured is compared with thedata of the levels measured in the past and found to be the same, thejoint can be estimated to be sound, and if larger, the joint can beestimated to be loose.

To estimate the looseness of a joint of a metallic pipe in reference tothe level of electromagnetic waves received, it is necessary that thereceiving conditions are the same as described above, and if the pipe ismetallic, it is of course necessary that such conditions as the distancefrom the receiving antenna, direction, etc. are the same and also thatthe characteristics of surroundings of the pipe buried underground orinstalled in a wall for electromagnetic waves are constant. Unless theseconditions are satisfied, it is difficult to estimate the looseness of ajoint in reference to the level of electromagnetic waves received.However, even if the pipe is buried, the looseness can be estimated whenall the above conditions are satisfied, and in the case of an exposedpipe for which receiving conditions can be easily made the same, theestimation is possible.

In the above inspection of joints, as described before, the transmittingantenna can also be arranged outside the pipe while the receivingantenna can be arranged inside the pipe for detecting theelectromagnetic waves entering through the joints from outside, needlessto say.

In the embodiment of the present invention described below, the locationof a leak portion such as a damaged portion like a corrosion hole orjoint of a pipe not exposed can be detected, and in addition, thedistance from a properly set reference location of the pipe to thedetected leak portion can be measured.

The embodiment is shown as a conceptual view in FIG. 15.

Symbol 1 denotes a pipe to be inspected. In this example, as in FIG. 7,the transmitting antenna 8 as an driving section is installed in thecover 24 of the central branch opening 23 of the Tee, to protrude theprobe 17 or loop (not illustrated) into the Tee 22. Symbol 43 denotes aprocessor, and the other parts are the same as in FIG. 7 and are giventhe same symbols to avoid double explanation.

In this configuration, on the transmitter 5 side, the transmittingantenna 8 drives electromagnetic waves in the pipe 1, and in this state,a worker on the receiver 6 side moves the antenna 10, to find theelectromagnetic waves leaking from the damaged portion 15 of the pipe 1.If the electromagnetic waves leaking from the damaged portion 15 such asa hole formed by corrosion in the pipe 1 are received, the location ofthe damaged portion 15 can be detected on the ground. If the antenna 10used is non-directional or weakly directional, the antenna 10 can bemoved along the pipe 1 (the route where the pipe 1 is estimated to beburied based on any information material such as drawing), and thelocation where the level of electromagnetic waves received becomes apeak can be detected as the location right above the damaged portion 15.When the antenna 10 used is sharply directional, the location rightabove the damaged portion can be detected at a high resolution, and theinfluence by external noise is also

As described above, symbol 43 denotes a processor, and the processor 43compares the electromagnetic waves transmitted by the transmitter 5 andthe electromagnetic waves detected by the receiver 6, to obtain thepropagation time of electromagnetic waves, and distance from the drivingplace, i.e., the transmitting antenna 8 installed at the open end of thepipe 1 to the damaged portion 15 where leak was detected by the receiver6.

To obtain the propagation time by comparing the electromagnetic wavestransmitted by the transmitter 5 with the electromagnetic waves detectedby the receiver 6, the transmitted electromagnetic waves are modulated.The electromagnetic waves can be modulated by any of various modulationmethods such as pulse modulation, amplitude modulation, frequencymodulation or code modulation, and the time difference between themodulated and transmitted electromagnetic waves and the receivedelectromagnetic waves can be measured or any proper known method such asdirect measurement, detection of phase difference or detection ofdeviation in the coefficient of correlation. In this case, the pulsecompression method used for improving S/N, etc. in radar and ultrasonicmeasurement can be applied, and the transmitted electromagnetic wavesare modulated by linear FM (chirp waves), barker code, M series code,complementary series code, etc.

In this configuration, the processor 43 commands to feed a signal Stmodulated as predetermined from the transmitter proper 7 through thecoaxial cable 12 to the transmitting antenna 8, for drivingelectromagnetic waves in the pipe 1 for propagation. Simultaneously, thesignal St similar to the driven electromagnetic waves is delivered tothe processor 43 for comparison with the received signal. On the otherhand, the signal Sr of electromagnetic waves leaking from the damagedportion 15 of the pipe and received by the receiver 6 is pre-processedto be amplified, etc. as required, and delivered to the processor 43 forcomparison with the transmitted signal.

The processor 43 compares the transmitted signal St with the receivedsignal Sr, and measures the time difference. The time difference can bemeasured by using any of proper methods stated above suitable for themodulation method adopted. For example, in the case of pulse modulation,the time difference between pulses can be directionally measured, and inthe case of amplitude modulation, the phase difference between themodulated transmitted signal St and the modulated received signal Sr canbe measured for calculating the time difference. For code modulation orany other proper modulation, the deviation in the coefficient ofcorrelation can be detected to calculate the time difference.

The time difference between the transmitted signal St and the receivedsignal Sr thus obtained includes the propagation time of electromagneticwaves corresponding to the route L from the transmitting antenna 8 tothe damaged portion 15 such as a hole formed by corrosion, thepropagation time corresponding to the route 1, from the transmitterproper 7 to the transmitting antenna 8, the propagation timecorresponding to the route l₂ from the transmitter proper 7 to theprocessor 43, the propagation time corresponding to the route l₃ fromthe antenna 10 through the receiver proper 9 to the processor 43, andthe propagation time corresponding to the route l₄ from the damagedportion l₅ to the antenna 10. Therefore, the time difference obtained isnot the propagation time of electromagnetic waves corresponding to theroute L from the transmitting antenna 8 to the damaged portion 15.

However, the propagation time of electromagnetic waves corresponding tothe routes l₁, l₂ and l₃ do not change, and can be measured beforehand,and the distance of the route l₄ is the sum of the buried depth of thepipe 1 and the height from the ground surface to the antenna 10. So, theformer can be known in reference to the piping work diagram, etc., andthe latter can be obtained by measurement. Therefore, the propagationtime of electromagnetic waves corresponding to the route L from thetransmitting antenna 8 to the damaged portion 15 can be obtained bysubtracting the propagation times of electromagnetic waves correspondingto the routes l₁, l₂, l₃ and l₄ from the time difference obtained by theabove measurement.

In this way, the propagation time of electromagnetic waves correspondingto the route L from the transmitting antenna 8 to the damaged portion 15can be obtained, and therefore, the distance of the route L can becalculated.

As described above, the location of the damaged portion such as a holeformed by corrosion in the pipe 1 can be detected on the ground bydetecting the electromagnetic waves leaking from the damaged portion 15,and the distance of the pipe 1 from the transmitting antenna 8 to thedamaged portion 15 can be obtained by comparing the electromagneticwaves received by the transmitter 6 with the electromagnetic wavesreceived by the receiver 5 as modulated signals, to measure the timedifference, and measuring the propagation time of electromagnetic wavesfrom the transmitting antenna 8 to the damaged portion 15 from the timedifference, etc. Therefore, the damaged portion 15 such as a hole formedby corrosion can be efficiently repaired, for example, by closing it bya resin, etc. using a pig, etc. from inside the pipe 1.

The following embodiment corresponds to FIGS. 16 to 18. In theinspection method for driving electromagnetic waves in a pipe with atransmitting antenna installed at a proper place in the pipe, or on thecontrary, in the inspection method for receiving the electromagneticwaves propagated in a pipe with a receiving antenna installed at aproper place in the pipe, the driven electromagnetic waves are changedover time not to form a fixed electromagnetic field distribution in thepipe.

For this purpose, the transmitter is provided with a means for changingthe frequency of driven electromagnetic waves over time in addition tothe basic components required for driving electromagnetic waves such asan oscillator and amplifier. FIGS. 16 to 18 typically show examples offrequency change over time. In FIGS. 16 and 17, the frequency iscontinuously changed by sweep in a certain range. In FIG. 16, thefrequency is changed as low→high, high→low, low→high, . . . In FIG. 17,the frequency is changed as low→high, low→high, low→high, . . . As ameans to obtain such frequency change over time, a sweep oscillator canbe used as the oscillator of the transmitter. In FIG. 18, the frequencyis changed in steps, and a means for obtaining such frequency changeover time, a programmable oscillator which allows plural oscillationfrequencies to be set can be used as the oscillator of the transmitter.

In general, if electromagnetic waves are driven and propagated in thepipe by the transmitter, magnetic field components in the pipe walldirection and electric field components in the direction perpendicularto the pipe wall cause the leak of electromagnetic waves at a damagedportion such as a hole formed by corrosion or a joint, etc. in the pipe,and the leaking electromagnetic waves are received by the receiverthrough the receiving antenna, to detect the damaged portion. However,electromagnetic waves of a certain frequency at a point of time may notform the above mentioned electric and magnetic field components at thecertain frequency, and at the point of time, leakage of electromagneticfields is hard to occur. Therefore, if the electromagnetic waves of sucha frequency are continuously driven, it is difficult to detect a damagedportion of a pipe in reference to the leaking electromagnetic waves.

However, in the configuration described above, since the frequency ofelectromagnetic waves driven in the pipe are changed over time, even ifelectric and magnetic field components hard to cause the leak from adamaged portion at a certain frequency at a point of time, theelectromagnetic field distribution is changed at a different frequencyat the next point of time, to cause electromagnetic waves to leak fromthe damaged portion, for allowing the detection of the damaged portion.

The following embodiment corresponds to FIGS. 19 to 21, and relates to amethod of detecting leaking electromagnetic waves by letting thereceiving antenna move along a pipe outside a piping system. In thisinspection method, when electromagnetic waves are received by thereceiver, whether they include those leaking from a leak portion orexternal noise only can be easily and reliably identified, andtherefore, the error detection of the leak portion can be prevented.

In this method, the transmitter proper 7 is provided with a drive ON-OFFcontrol means 44 and a receiving means 45 for receiving the controlsignal of the ON-OFF control means. The ON-OFF control means 44 can becomposed to turn on and off the oscillator or turn on and off the waveguiding channel or in any other proper way. On the other hand, thereceiver proper 9 is provided with a remote control switch for turningon and off the ON-OFF control means 44 of the transmitter proper 7, inaddition to the basic components required for receiving electromagneticwaves such as a detector, amplifier, signal processor, and receivedsignal level indicator, and the remote control switch is composed of acontrol switch 46 and a switch state transmitting means 47. Thetransmitting means 47 and the receiving means 45 are expressed aswireless communication means in the drawings, but they can also be wiredcommunication means, needless to say.

In this configuration, the worker on the transmitter proper 7 sideinstalls the transmitting antenna 8 to the Tee 22 provided on theextension of, for example, a gas pipe 1 to be inspected foridentification of damaged portions such as leak portions, and connectthe transmitting antenna 8 with the transmitter proper 7 for actuatingit. The worker on the receiver proper 9 side operates the control switch46, and sends an ON command from the transmitting means 47 to the ON-OFFcontrol means 44 through the receiving means 45 of the transmitterproper 7, to turn on the drive of electromagnetic waves in thetransmitting antenna 8. The worker moves the receiving antenna 10 tosearch for electromagnetic waves, watching the level of electromagneticwaves received and indicated on the indicator of the receiver proper 9.

In this search, when a portion where the indicated level becomes high isdetected, the worker operates the control switch 46, to send an OFFcommand to the ON-OFF control means of the transmitter proper 7, to turnoff the drive of electromagnetic waves in the transmitting antenna 8. Inthis case, if the electromagnetic waves received in ON state contain theelectromagnetic waves leaking from the damaged portion 15 of the pipe 1,the indicated level declines as shown in FIG. 21(b) when the drive isturned off. On the other hand, when the electromagnetic waves receivedin ON state do not contain the electromagnetic waves leaking from thedamaged portion 15 of the pipe and are external noise only, theindicated level does not change as shown in FIG. 21(a) even if the driveis turned off. Therefore, if the indicated level in OFF state iscompared with the indicated level in ON state, the leakingelectromagnetic waves can be identified, and the damaged portion can bedetected in reference to the leaking electromagnetic waves. Thecomparison between OFF state and ON state in indicated level can be doneby a worker or can also be automated.

FIG. 20 typically shows another configuration to which the method of thepresent invention is applied. The same components as in FIG. 19 aregiven the same symbols to avoid double explanation.

In this example, the transmitter proper 7 is provided with an ON-OFFcontrol means to turn on and off the drive of electromagnetic waves byitself, and a transmitting means 49 for the signals synchronous with theON and OFF actions. On the other hand, the receiver proper 9 is providedwith a receiving means 50 for receiving the signals synchronous with theON and OFF actions, to indicate the action state.

In the configuration of FIG. 29, on the transmitter proper 7 side, thedrive is turned on and off at time intervals preset in a memory means,etc., and on the receiver proper 9 side, the synchronous signaltransmitted from the transmitter proper 7 side is received, to indicatethe ON or OFF state of drive. Therefore, when the worker on the receiverproper 9 side detects a location where the indicated level is highduring his search, as in the case of FIG. 19 in reference to the ON andOFF states of drive and the indicated level, he can detect whether theelectromagnetic waves received contain the electromagnetic waves leakingfrom the damaged portion 15 of the pipe 1, by comparing the indicatedlevel in OFF state and the indicated level in ON state.

In the respective methods described above, the electromagnetic wavestransmitted from the transmitter are propagated in the pipe concerned ofa piping system at a frequency higher than the cut-off frequency for thepipe used as a wave guiding channel of electromagnetic waves, but in thefollowing two embodiments, the frequency is kept lower than the cut-offfrequency.

One of the embodiments is shown in FIG. 22. In this embodiment, thetransmitting antenna 8 of the transmitter 5 is moved by a cable 51, etc.in the pipe 1 to be inspected of a piping system, while electromagneticwaves of a frequency lower than the cut-off frequency for the pipe usedas a wave guiding channel of electromagnetic waves, and the receivingantenna 10 of the receiver 6 is moved in relation with the movement ofthe transmitting antenna 8, to receive leaking electromagnetic waves,for inspecting the elements of the piping system. In reference to thelocation of the transmitting antenna 8 at which the level ofelectromagnetic waves received by the receiver becomes a peak, thelocation of the element concerned of the piping system is detected.

For such inspection, on the transmitter 5 side, the transmitter proper 7the transmitting antenna 8 connected to the transmitter proper 7 by thecable 51 acting also as a long antenna wire, and an unwinder 52 and awinder 53 for the cable 51 are installed.

In this configuration, the cable 51 is delivered by the unwinder 52, tomove the transmitting antenna 8, or the cable 51 is wound by the winder53, to move the transmitting antenna 8, while electromagnetic waves of afrequency lower than the cut-off frequency of the pipe 1 aretransmitted. Simultaneously, the receiving antenna 10 composed asdescribed above is moved in relation with the movement of thetransmitting antenna, to receive the electromagnetic waves leaking froma damaged portion, or joint, etc. of the pipe 1.

The electromagnetic waves from the transmitting antenna 8 are notpropagated in the pipe 1 and attenuated greatly in a short distance. So,the quantity of electromagnetic waves leaking from a location concernedsuch as the damaged portion 15 or joint of the pipe is largest when thetransmitting antenna 8 is nearest to the location concerned. Therefore,the level of electromagnetic waves received by the receiver 6 throughthe receiving antenna 10 changes very greatly when the antenna is nearthe location concerned, to make the peak more outstanding. So, thelocation concerned can be detected at higher accuracy in reference tothe peak. Furthermore, since the frequency can be kept low as describedabove, the electromagnetic waves are attenuated less by the soil, etc.around the buried pipe, to enhance the receiving sensitivity.

In the other embodiment, the transmitter and the receiver in the aboveembodiment are arranged reversibly. In this method, though notillustrated, the transmitting antenna of the transmitter is moved alongthe pipe outside the piping system to be inspected of a piping system,while electromagnetic waves of a frequency lower than the cut-offfrequency for the pipe used as a wave guiding channel of electromagneticwaves are transmitted from outside the piping system, while theelectromagnetic waves entering the pipe from outside are received forinspection of elements of the piping system. In reference to thelocation of the receiving antenna where the level of electromagneticwaves received by the receiver becomes a peak, the location concerned ofan element of the inspected piping system is detected.

In this case, since the electromagnetic waves entering from thetransmitting antenna through the location concerned are not propagatedin the pipe, the level of electromagnetic waves becomes highest when thereceiving antenna is nearest to the location concerned. Therefore, alsoin this case, the level of electromagnetic waves received by thereceiving antenna changes very greatly when the antenna is near thelocation concerned, to make the peak more outstanding, for enhancing theaccuracy in the detection of the location concerned in reference to thepeak.

Furthermore, these methods can also measure the route length of thepiping system by allowing the length of the cable delivered to move theantenna in the pipe to be measured by the unwinder, etc.

Also in these two methods, as in the methods described before, ifelectromagnetic waves as carrier waves are modulated by any properinformation signals, whether the electromagnetic waves received arethose transmitted by the transmitter or noise can be easilydistinguished.

Moreover, in the method of moving the receiving antenna outside thepipe, if the method of turning on and off the electromagnetic wavestransmitted for receiving by the receiver is applied, the influence ofexternal noise can be decreased.

In the following embodiment, the frequency of electromagnetic waves iskept at lower than the cut-off frequency of the pipe as in the above twoembodiments, but the receiving antenna or the transmitting antennaarranged in the pipe is made long to eliminate the necessity ofmovement.

FIG. 24 conceptually shows the method. As described before, a longtransmitting antenna 54 with many radiating parts directional in thedirections perpendicular to the axis connected in the axial direction isinserted in the pipe 1 in the testing range, and electromagnetic wavesare radiated from these radiating parts. In this state, the receivingantenna, and as required the receiver proper 9 are moved along the pipe1 in the testing range, for searching for leaking electromagnetic waves.

Since the long transmitting antenna 54 with many radiating partsdirectional in the directions perpendicular to the axis connected in theaxial direction is inserted in the testing range of the pipe 1, toirradiate electromagnetic waves from the respective radiating parts, thereceiving antenna 10 only can be moved along the pipe outside the pipein the testing range, to search for the leaking electromagnetic waves.Since the electromagnetic waves are not required to be propagated in thepipe which can be act as a circular wave guiding channel, the frequencyused is not limited to be higher than the cut-off frequency for thecircular wave guiding tube.

Therefore, the advantage attributable to the low frequency ofelectromagnetic waves used, that attenuation by soil, etc. can be keptsmall can be obtained.

The long transmitting antenna 54 used in this method can be a leakagecoaxial cable or twisted pair leakage cable as used for mobilecommunication in a tunnel, etc. Such a cable can be inserted into thepipe 1, using an insertion mechanism, etc. which can be a conventionallywidely used drive cable for an in-tube tester, etc. with the gas pipekept active.

Furthermore, the long transmitting antenna 54 can keep the length of onehelical turn very smaller than the wavelength of the electromagneticwaves radiated or can keep the length of one helical turn at n times thewavelength (n is an integer of 2 or more) with its directionality keptin a direction perpendicular to the axis. A cable obtained by coveringthe helical wire with an insulator can be treated like the abovementioned cables.

Moreover, the transmitting antenna 54 can also be formed by connectingmany small antennas to form a cable.

In the above method, the transmitting antenna is long and arranged inthe pipe, but the receiving antenna can be made long and arranged in thepipe, while the transmitting antenna is moved outside the pipe along thepipe, for transmitting electromagnetic waves.

In these two methods, as done in the other methods described before, ifthe electromagnetic waves as carrier waves can be modulated by properinformation signals, whether the electromagnetic waves received are theelectromagnetic waves transmitted by the transmitter or noise can beeasily distinguished. Furthermore, the level of electromagnetic wavesreceived and the receiving sensitivity can also be properly adjusted.

When the receiving antenna is moved outside the pipe, the transmittedelectromagnetic waves can be turned on and off to be received by thereceiver, for decreasing the influence of external noise.

INDUSTRIAL APPLICABILITY

Since the present invention is as described above, if the piping systemto be inspected is, for example, a city gas supply system, the leak ofgas from a gas pipe is detected in reference to the electromagneticwaves leaking from a point where gas leak occurs, not in reference tothe gas leak. Therefore, the present invention is useful to accuratelydetect the point of gas leak, and can also be applied to detect thelocations of other elements such as joints of the piping system and alsothe lengths of routes. The present invention can also be applied fordetecting damaged portions, etc. of pipes of various piping systems.

We claim:
 1. A method for detecting and locating faults and leaks in anexisting underground piping system using electromagnetic waves,consisting essentially of:moving a transmitting antenna of a transmitteroutside the piping system along the direction of a pipe to be inspected,while transmitting electromagnetic waves from said transmitting antennaoutside the piping system; receiving said electromagnetic waves whichenter the piping system from outside by means of a a receiving antennainstalled at a proper place in the pipe, said receiving antenna beingconnected to a receiver; and detecting and locating any faults and leaksin the piping system being inspected by observing any peaks in the levelof received electromagnetic waves which occurs when the transmittingantenna is located nearest the location of faults and leaks in the pipebeing inspected.
 2. The method for detecting and locating faults andleaks in an existing underground piping system using electromagneticwaves, according to claim 1, wherein the frequency of theelectromagnetic waves is changed over time.
 3. The method for detectingand locating faults and leaks in an existing underground piping systemusing electromagnetic waves, according to claim 1, wherein reception ofentering electromagnetic waves by the receiver is effected when thetransmission of electromagnetic waves by the transmitter is in ON state,and is effected also when the drive of electromagnetic waves by thetransmitter is temporarily in OFF state, and the signals received in OFFstate are compared with the signals received in ON state, to distinguishthe electromagnetic waves transmitted by the transmitter.
 4. The methodfor detecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to claim 1, whereinthe electromagnetic waves entering the piping system from outside to bepropagated by the transmitter in the piping system inspected aremodulated.
 5. The method for detecting and locating faults and leaks inan existing underground piping system using electromagnetic waves,according to claim 1, wherein the electromagnetic waves entering thepiping system from outside to be propagated by the transmitter in thepipe of the piping system are modulated; the electromagnetic wavesreceived by the receiver are compared with the electromagnetic wavestransmitted by the transmitter as modulated signals, to obtain the timedifference; and the propagation time corresponding to the distancecorresponding to the propagation distance from the receiving point tothe leak point is subtracted from the time difference, to measure thepropagation time of electromagnetic waves from the driving point to theleak point, for obtaining the distance of the piping system from thereceiving point to the leak point.
 6. The method for detecting andlocating leaks and faults in an existing underground piping system usingelectromagnetic waves, according to claim 1, wherein the transmitter isprovided with an adjusting device for adjusting the intensity of theelectromagnetic waves transmitted by it.
 7. The method for detecting andlocating faults and leaks in an existing underground piping system usingelectromagnetic waves, according to claim 1, further comprising drillinga hole in the wall of the pipe of the piping system to be inspected,forming internal threads in said pipe to form an antenna installationhole; and installing a coaxially formed antenna with a probe protrudedat the center and with external threads formed around an outside memberin the antenna installation hole with the internal and external threadsengaged with each other, to locate the probe in the pipe, forconstituting an antenna.
 8. The method for detecting and locating faultsand leaks in an existing underground piping system using electromagneticwaves, according to claim 1, further comprising cutting off an end ofthe pipe of the piping system to be inspected, and installing acoaxially formed antenna with a probe protruded coaxially in the coverclosing the end, said cover being installed at the end for constitutingan antenna.
 9. The method for detecting and locating faults and leaks inan existing underground piping system using electromagnetic waves,according to claim 1, further comprising installing a probe to protrudeinside a cover closing a central branch opening of a Tee installed on anextension of the pipe to be inspected of the piping system; andconnecting the probe and an electromagnetic wave oscillator by a coaxialcable; said probe being located in the Tee with the cover installed atthe central branch opening, to constitute an antenna.
 10. The method fordetecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to claim 9, whereinthe cover is threadedly engaged with the central branch opening of theTee, and positioning a shielding material shaped like an O ring betweenthe cover and the central branch opening of the Tee.
 11. The method fordetecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to claim 9, whereinthe cover is threadedly engaged with the central branch opening of theTee, and a shielding material is provided in the threadedly engagedportion.
 12. The method for detecting and locating faults and leaks inan existing underground piping system using electromagnetic waves,according to claim 1, further comprising protruding a loop inside acover closing a central branch opening of a Tee installed on anextension of the pipe of the piping system to be inspected; andconnecting the loop and an electromagnetic wave oscillator by a coaxialcable; wherein a probe is located in the Tee with the cover installed atthe central branch opening, to constitute an antenna.
 13. The method fordetecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic wave, according to claim 12, whereinthe cover is threadedly engaged with the central branch opening of theTee, and further comprising providing a shielding material shaped likean O ring between the cover and the central branch opening of the Tee.14. The method for detecting and locating faults and leaks in anexisting underground piping system using electromagnetic waves,according to claim 12, wherein the cover is threadedly engaged with thecentral branch opening of the Tee, and further comprising providing ashielding material in the threadedly engaged portion.
 15. The method fordetecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to claim 12,wherein the loop has its axial direction kept in the axial direction ofthe Tee.
 16. The method for detecting and locating faults and leaks inan existing underground piping system using electromagnetic waves,according to claim 12, wherein the loop has its axial direction kept inthe tangential direction of the inside circle of the Tee.
 17. The methodfor detecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to claim 1, whereinthe frequency of electromagnetic waves is continuously changed by sweep.18. The method for detecting and locating faults and leaks in anexisting underground piping system using electromagnetic waves,according to claim 1, wherein the frequency of electromagnetic waves isstepwise changed.
 19. The method for detecting and locating faults andleaks in an existing underground piping system using electromagneticwaves, according to claim 1, wherein the transmitter is provided with anelectromagnetic wave drive ON-OFF control means, to operate the ON-OFFcontrol means on the receiver side.
 20. The method for detecting andlocating faults and leaks in an existing underground piping system usingelectromagnetic waves, according to claim 1, wherein the transmitter isprovided with an electromagnetic wave drive ON-OFF control means, toeffect ON-OFF control by itself, and signals synchronous with the ON-OFFactions are transmitted to the receiver, to allow the receiver to detectthe ON-OFF states.
 21. The method for detecting and locating faults andleaks in an existing underground piping system using electromagneticwaves, according to claim 1, wherein the electromagnetic waves aremodulated by human recognizable information signals.
 22. The method fordetecting and locating faults and leaks in an existing undergroundpiping system using electromagnetic waves, according to wherein the timedifference is measured in reference to the phase difference between theelectromagnetic waves detected by the receiver and the electromagneticwaves transmitted by the transmitter in terms of modulated signals. 23.The method for detecting and locating faults and leaks in an existingunderground piping system using electromagnetic waves, according toclaim 1, wherein in the transmission of electromagnetic waves by thetransmitter and the reception of electromagnetic waves by the receiver,the pulse compression method is applied.
 24. The method for detectingand locating faults and leaks in an existing underground piping systemusing electromagnetic waves, according to claim 1, wherein an adjustingdevice is adjusted in response to the level of electromagnetic wavesreceived by the receiver.
 25. The method for detecting and locatingfaults and leaks in an existing underground piping system usingelectromagnetic waves, according to claim 1, wherein the piping systemsto be inspected include underground pipes, and locations to be detectedare damaged portions such as holes formed by corrosion in the pipes. 26.The method for detecting and locating faults and leaks in an existingunderground piping system using electromagnetic waves, according toclaim 1, wherein the elements of the piping system to be inspected arein exposed joints, and the locations to be detected are the locations ofthe joints themselves.
 27. The method for detecting and locating faultsand leaks in an existing underground piping system using electromagneticwaves, according to claim 1, wherein the level of electromagnetic wavesreceived by the receiver is referred to for estimating the state of eachjoint to be inspected.
 28. The method for detecting and locating faultsand leaks in an existing underground piping system using electromagneticwaves, according to claim 27, wherein the electromagnetic waves enteringthe pipe from the joint to be inspected are received by the receiver, todetect the location of the joint, and the level of the electromagneticwaves received is referred to for estimating the state of the joint.